High-frequency amplifier and oscillator



Aug. 5, 1947.' L. N. BRxLLoUlN HIGH vFREQUENCY AMPLIFIER yANDlOSCILLATOR Filedvmarch 2o, 1942 2 sheets-sheet 1 mm ms@ y @wwnmw .xw i

INVENToR. fw/ /v. /Lww/v ATIURLTY ug. 5, 1947. l L. N. BRILLOUIN2,424,965

I HIGH FREQUENCY AMPLIFIER AND OSCILLATOR Filed March 20, 1942 2sheets-sheet 2 Amma-Y Patented Aug. 5, 194i? einem HIGH-FREQUENCYAMPLIFEER AND OSCILLATOR Leon N. Brillouin, Madison, Wis., assignor toFederal Telephone and Radio Corporation, a

f corporation of Delaware Application March 20, 1942, Serial No. 435,521

8 Claims.

This invention relates to electron discharge apparatus and moreparticularly to such apparatus intended for the amplification andgeneration of high frequency electrical waves,

It is well known that in conventional electron discharge tubes thefinite electron transit time prevents efcient operation at very highfrequencies due to abnormal loading of the input circuit and consequentloss of transconductance of the tube, excessive coupling between theinput and output circuits and increased losses due to the presence oflarge circulatory currents at high frequencies.

The principal object of my invention is to provide an improved electrondischarge apparatus particularly suitable for use as an amplifier oroscillator at high frequencies.

More particularly, it is an object of my invention to provide anelectron discharge device in which electron transit time is notcritically related to the period of oscillation and in which highfrequency losses are minimized.

The various objects and features of my invention will be more fullyunderstood from the following detailed description of certainembodiments as shown in the accompanying drawings in which Fig. 1 is adiagram employed to illustrate the principle upon which my invention isbased;

Fig. 2 is a side-sectional View of an electron discharge apparatusshowing one typical method of carrying my invention into effect;

Figs. 2A, 2B, and 2C illustrate the connes of the electron beam producedby the apparatus shown in Fig. 2;

Fig. 3 illustrates alternative electrode structures which may be used inplace of the electrodes shown in Fig, 2;

Figs, 3A, 3B, and 3C illustrate the confines of the electron beamproduced in the arrangement of Fig. 3;

Fig. 4 shows a side sectional view of an electron discharge apparatusaccording to the present invention;

Fig. 5 shows a still further electrode arrangement; and

Figs. 5A and 5B illustrate the confines of the electron beam produced bythe arrangement of Fig. 5.

Theoretical investigations made by myself (Physical Review, vol. 60,1941, p. 385) and by J. P. Blewett and S. Ramo (Physical Review, vol.57, 1940, p. 365) have shown the formation and type of motion of anelectron beam traveling inside a metallic pipe under the action of alongitudinal magnetic field. Referring to Fig. 1, a metallic cylinder Cis maintained at a positive potential and a constant magnetic field H isgenerated parallel to the axis Z of the cylinder C. Electrons enter thecylinder C with a certain longitudinal velocity o2 and rapidly build upan electronic cloud of constant density Pu whichrotates about the axis Zwith a constant angular velocity wn: then WLLOHZ PO- 26W where erepresents the charge of the electron, m is the mass of the electron and,u0=% 1020 in electrostatic units, an is Larmors angular velocity.

Each electron describes a helix around the axis Z, due to thesuperposition of the constant velocity o2 and of the rotation wn. Thespace charge density Po is uniform throughout the beam and the wholeelectronic cloud moves like a solid body, gliding along the axis Z witha velocity o2, and at the same time spinning about the axis Z of the-cylinder C with the angular velocity wn. This represents the stabletype of motion of the electron beam.

I have found that by producing periodic changes in the cross-sectionalform or area of such a beam, radial vibrations are impressed upon it andresult in oscillations which may be used for the purpose ofamplification or generation of high frequency waves.

' A feature of my invention resides, therefore, in the provision of anelectron discharge apparatus comprising a means for forming theelectrons emitted by a source into a beam comprising an electronic cloudof normally constant density Which rotates about a linear axis 'with aconstant angular velocity and which simultaneously advances lalong thisaxis, and means for producing periodic changes in the cross sectionalform or area of the beam at a predetermined point along the axis, meansalso being provided for extracting energy from the beam at anotherpredetermined pcint along the axis.

Reference should now be made to Fig. 2, which shows one method ofcarrying out my invention. At one end of an evacuated envelope B thereis mounted an electron emissive cathode K and a beam focusing andconcentrating electrode F. A metal cylinder C is mounted in the envelopeB parallel to the major axis of the envelope B, and a target orcollector electrode T is mounted at the end of the cylinder C remotefrom the cathode K. Surrounding the envelope B and the cylinder C is acoil M for producing a magnetic field parallel to the axis of themetallic cylinder C. Near the entrance to the cylinder C adjacent thebeamforming electrodes K, F is mounted a rst cylindrical electrode C1,the radius of which is slightly greater than the radius of the beam,whereby under normal conditions electrons will not strike this electrodeand no current will flow to it. A second cylindrical electrode C2 ismounted within the cylinder C and adjacent its other end, such secondcylinder C2 also having a radius slightly greater than the radius of theelectron beam. The cylinder C is maintained at a high positive potentialwith respect to the cathode. The focusing electrode F is also maintainedat a positive potential as is customary in electron guns, whilst thecollector or target electrode I is maintained preferably at a slightlypositive potential with respect to the cathode. An input circuit L1 isconnected to the electrode C1, and an extracting circuit is connected tothe electrode C2.

If an oscillating voltage is applied to the electrode C1 from thecircuit L1, alternate radial expansions and compressions will beimpressed upon the electronic beam. Fig. 2A illustrates the confines ofthe electronic beam in the stable condition. Fig. 2B illustrates theconnes of the beam at the point where it is under the inuence of theelectrode C1 when a positive half cycle is impressed thereon, and Fig.2C illustrates the confines of the beam when under the iniluence of anegative half cycle impressed upon the electrode C1. These alternatingradial vibrations travel along the beam moving in the direction of theaxis Z with the longitudinal velocity v2. Since the radius of the crosssection of the beam is periodically greater than the radius of theelectrode C2 groups of electrons will hit this electrode C2, and yieldan alternating current on it. The oscillations or vibrations impressedupon the electron beam by the electrode C1 will be large if theirfrequency is correctly related to the angular velocity of the beam. Ihave found that the frequency corresponding to the type of motiondescribed with reference to the arrangement shown in Fig. 2 is about V2times Larmors frequency (w=\/'2 on) With the arrangement of Fig. 2, theradial vibrations impressed upon the electronic beam o occursimultaneously in all directions of one cross section. Each crosssection of the beam remains circular, but the radius of this circle isalternately larger and smaller than the normal radius of the beam. Thecross section of the beam may, however, be periodically deformed by theuse of other forms of electrodes. If, for example, the electrodes withinthe cylinder C are in the form of sets of four arcuate plates A1, Az,A3, A4, and B1, B2, Bs, B4, as shown in Fig. 3 the four in each setbeing disposed on each side of the electron beam, A1 opposite A2, A3opposite A4, etc., the cross vsection of the beam during onefhalf cycleof an oscillation impressed upon the electrodes A1, A2 will be anellipse with its major axis horizontal, as shown in Fig. 3B, and duringthe succeeding half-cycle will be an ellipse with its major axisvertical, as shown in Fig. 3C. These elliptic oscillations travel alom,rthe beam within the cylinder C, and simultaneously rotate about the axisZ in accordance with the motion of the electron beam as described withreference to Fig. l. Before leaving the cylinder C, the beam passesbetween the electrodes B1, B2, and if the longitudinal velocity of thebeam, the angular Velocity on, and the frequency of the oscillationsimpressed upon the electrodes A1, A2 are correctly chosen, the ellipticoscillations of the beam will result in a current on the electrodes B1,B2, since groups of the deiiected electrons will strike theseelectrodes.

In Fig. 3, the electrode pairs A1, A2, and B1, B2, have been shownmounted on parallel diameters of the cylinder C. To avoid directcapacity effect between the pairs of electrodes A1, A2, and B1, Ba, itis preferable to arrange these pairs of electrodes along diameters atright angles to one another. As in the preceding embodiments, thefrequency of the impressed vibrations should be correctly related to theangular velocity of the electron beam.

In Figure 4 the cylinder C and the A and B electrodes enclosed thereinas diagrammed in Fig. 3 are shown in an envelope B similar to that shownin Fig. 2 with the connections therethrough to cathode K, electrode F,and plate T, and the solenoid M therearound to make a more completeshowing of the electron discharge device according to this invention.The figure contains elements of Figs. 2 and 3 and corresponding partshave been labeled accordingly.

More complicated structures may be used for the beam deforming andenergy extracting electrodes. Each of these electrodes may beconstituted by 4, 6 211. arcuate plates disposed on a circle in order toexcite vibrations of more complex types along the electron beam. Fig. 5shows one example of such an arrangement in which the electrodestructure upon which the input oscillations are impressed comprises sixarcuate sections, alternate sectors being connected to one side of theinput circuit and the remaining sectors being connected to the otherside of the input circuit. The energy extracting electrode structure issimilarly constituted and connected.

to the energy extracting or output circuit. With such an arrangement thecross section of the electron beam is alternately deformed according tothe two shapes shown in Figs. 5A and 5B.

The arrangements described will function as ampliers of high frequencyWaves. If, however, a coupling is provided between the input circuit L1and the output circuit Le as shown by the dotted line arrow in Fig. 2and Fig. 4, oscillations will be fed back from the output circuit L2 tothe input circuit L1 and will build up, causing the Y device to generatehigh-frequency oscillations which may be extracted from the outputcircuit Lz.

While I have described my invention with reference to particularembodiments thereof, it will be understood that other modifications maybe made by those skilled in the art without departing from the inventionas defined in the appended claims.

What I claim is:

1. An electron discharge apparatus for amplifying a variable voltagecomprising an envelope, means including a cathode positioned within saidenvelope for producing and directing an electron beam, a metallic tubepositioned axially about the path of said beam within said envelope,means positioned about said tube for generating a magnetic eld parallelto the axis of said tube whereby said beam is rotated about the linearaxis with a constant velocity, means connected to said tube formaintaining said tube at a positive potential with respect to saidcathode whereby said beam is advanced through said tube, a first pair ofoppcsitely directed arcuate electrodes disposed one on either side ofthe path of said beam and mounted in said tube adjacent the end nearestthe cathode, a second pair of oppositely directed arcuate electrodesdisposed one on either side oi the path of said beam and mounted in saidtube at a point along axis from said rst pair of electrodes, a variableVoltage source connected to said fir 'pair of electrodes for controllinga radial dim n ,ci said beam, and an output circuit connected to saidsecond pair of electrodes for extracting energy irom said beam in theform of said variable voltage 2. Electron discharge apparatus accordingto claim 1, in which said rst pair of electrodes are turned 90 aboutsaid beam with respect to said second pair of electrodes.

3. An electron discharge apparatus for amplifying alternating currentwaves comprising, an envelope, means including a cathode positionedwithin said envelope for producing and directing an electron beam, ametallic tube positioned axially about the path oi said beam within saidenvelope, means adjacent said tube for generating a magnetic neldparallel -to the axis of said tube whereby said beam is rotated about alinear axis with a constant velocity, means connected to said tube formaintaining said tube at a positive potential with respect to saidcathode whereby said beam is advanced through said tube at a constantvelocity, an even number greater than two of rst electrodes mounted insaid tube adjacent the end nearest the cathode and disposedsubstantially in a circle about said beam, an even number greater thantwo of second electrodes mounted within said tube, longitudinally fromsaid first electrodes and also disposed substantially in a circle aboutsaid beam, an input lcircuit having two terminals, one or" which isconnected to alternate rst electrodes and the other of which isconnected to the remaining iirst electrodes for periodically deformingthe path of rotation of said beam, and an output circuit having twoterminals, one of which is connected to alternate second electrodes andthe other of which is connected to the remaining second electrodes forextracting energy from said beam in the form .of said alternatingcurrent waves.

4. An electron discharge apparatus comprising a metallic tube, meansadjacent said tube for producing a substantially solid, generallycylindrical electron ibeam and directing it axially through said tube,means positioned in the vicinity of said metallic tube for generating amagnetic eld parallel to the axis of the said tube whereby said beam isrotated, a rst electrode mounted in said tube along the path or saidbeam, electrodes mounted within said tube and spaced from and co-axialwith said rst electrode and normally outside the path of said beam, aconnection to said iirst electrode for applying thereto a variablevoltage of frequency different from and bearing a predetermined relationto the frequency of the rotation of said beam for periodically deformingthe path of rotation of said beam whereby electrons periodically strikesaid electrodes, and an energy extracting circuit connected to saidelectrodes adapted to remove energy from said electron beam.

5. Electron discharge apparatus comprising, an envelope, a metallic tubewithin said envelope, means in said envelope for producing an electronbeam having a predetermined cross-sectional area and for directing saidbeam axially through said tube, means positioned in the vicinity of saidmetallic tube for generating a magnetic iield parallel to the axis ofsaid tube whereby said beam is rotated, radially displaced electrodesmounted in said tube in a position about the path of said electron beam,means positioned in said tube intermediate said electrodes and said beamproducing means for periodically enlarging the crosssectional area ofsaid beam at a frequency dii ferent from and bearing a predeterminedrelation to the frequency of the rotation of said beam whereby electronsperiodically strike said electrodes, and an energy extracting circuitconnected to said electrodes.

6. Electron discharge apparatus comprising an envelope, a metallic tubewithin said envelope, means in said envelope for producing an electronbeam having a predetermined cross-sectional shape and for directing saidbeam axially through said tube, means positioned about said tube forgenerating a magnetic field parallel to the axis of said tube wherebysaid beam is rotated, electrodes mounted in said tube in a positionnormally outside the path of said electron beam, means in said tubeintermediate said electrodes and said beam producing means forperiodically deforming the cross-sectional shape of said beam at afrequency different from and Ibearing a predetermined relation to thefrequency of the rotation of said beam whereby electrons periodicallystrike said electrodes, and an energy extracting circuit connected tosaid electrodes.

'7. Electron discharge apparatus for generating high frequencyoscillations comprising, an envelope, means in said envelope forproducing and generally directing an electron beam including a biasingelectrode, a metallic tube positioned about the path of said beam, meanspositioned about said tube for generating a magnetic eld parallel to theaxis of said ltube for substantially the entire length ci said beamwhereby said beam is rotated, a iirst electrode mounted Within said tubeand within said envelope, a second electrode mounted within said tubeintermediate said first electrode and said beam producing means, aresonant input circuit connected to said second electrode forcontrolling a radial dimension of said beam, said resonant input circuitbeing tuned to a frequency diierent from and bearing a predeterminedrelation to the frequency of the rotation of said beam, a resonantextracting circuit connected to said first electrode, and meansconnected to said input and extracting circuits coupling said input andextracting circuits whereby said high frequency oscillations aregenerated and extracted.

S. An electron discharge apparatus comprising an envelope, a metallictube within said envelope, means positioned in the vicinity of said tubeand including a cathode for producing an electron beam and directingsaid beam through said tube, means positioned in the vicinity of saidtube for rotating said beam about a linear axis with a normally constantvelocity, a first pair of oppositely directed arcuate electrodesdisposed one on either side of the path of said beam and mounted in saidtulbe adjacent the end nearest the cathode, a second pair of oppositelydirected arcuate electrodes disposed one on either side of the path ofsaid beam and mounted in said tube at a'point along its axis removedfrom said rst pair of electrodes and turned about said axis lwithrespect to said first pair of electrodes, a variable voltage sourceconnected to said iirst pair of electrodes for controlling a radialdimension of said beam whereby electrons periodically strike said secondpair of electrodes, and an output circuit connected to said second pairof electrodes for extracting energy from said beam in the form of saidvariable voltage.

The following references are of record in the LEON N. BRIILOUIN.

REFERENCES CITED file of this patent:

Number UNITED STATES EATENTS Name Date Haei i Dec. 15, 1936 Number

